The long-term goal of the proposed research is to understand how calcium, a universal messenger, regulates gene expression and cell activities. Calcium ions are pivotal in the regulation of a variety of cellular processes. Abnormal calcium homeostasis has been implicated in aging and in numerous human diseases, such as Alzheimer's disease. The enduring regulatory effects of calcium depend on changes in gene expression. The mechanisms by which cells decode the information carried by calcium signals and convert them into distinct alterations in gene expression is poorly understood. A prevailing model is that Ca2+ entry through different ion channels activates distinct transcription factors. Through the mediation of a series of protein kinases or phosphatases, Ca2+/calmodulin stimulates a range of transcription factors. Recent bioinformatic analyses have suggested the existence of transcription factors that are activated directly by Ca2+/calmodulin, which could respond to Ca2+ signals more quickly. A group of candidates, the calmodulin-binding transcription activators (CAMTAs) were recently identified in plants. Their homologs in animals have yet to be studied. We have isolated two Drosophila mutant alleles of dCAMTA, the fly CAMTA gene, and detected a strong and consistent phenotype in these mutants that implies an impaired deactivation of the fly light-stimulated Ca2+ channel TRP. Therefore we plan to use the fly photoreceptor cells as an assay system to study this new group of Ca2+-regulated transcription factors. A combination of molecular and cell biological, genetic, electrophysiological and calcium imaging approaches will be used to: 1. Test the hypothesis that dCAMTA is activated through Ca2+/calmodulin-binding in vivo. 2: Test the hypothesis that dCAMTA exists in the cytoplasm and translocates into the nuclei upon activation. 3: Test the hypothesis that dCAMTA proteins form homomultimers. 4. Test the hypothesis that dCAMTA depends on TRP channels for activation in the photoreceptor cells. 5. Test the hypothesis that the loss of dCAMTA function leads to increased Ca2+ level in the photoreceptor cells. 6. Determine the target genes of dCAMTA.